/*
Copyright (C) 1997-2001 Id Software, Inc.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/* crc.c */

#include "client.h"

// this is a 16 bit, non-reflected CRC using the polynomial 0x1021
// and the initial and final xor values shown below...  in other words, the
// CCITT standard CRC used by XMODEM

#define CRC_INIT_VALUE  0xffff
#define CRC_XOR_VALUE   0x0000

static const uint16_t crctable[256] = {
    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
    0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
    0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
    0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
    0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
    0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
    0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
    0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
    0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
    0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
    0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
    0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
    0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
    0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
    0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
    0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
    0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
    0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
    0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
    0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
    0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
    0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
    0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
    0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
    0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
    0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
    0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
};

static uint16_t CRC_Block(byte *start, size_t count)
{
    uint16_t    crc = CRC_INIT_VALUE;

    while (count--)
        crc = (crc << 8) ^ crctable[(crc >> 8) ^ *start++];

    return crc;
}

static const byte chktbl[1024] = {
    0x84, 0x47, 0x51, 0xc1, 0x93, 0x22, 0x21, 0x24, 0x2f, 0x66, 0x60, 0x4d, 0xb0, 0x7c, 0xda,
    0x88, 0x54, 0x15, 0x2b, 0xc6, 0x6c, 0x89, 0xc5, 0x9d, 0x48, 0xee, 0xe6, 0x8a, 0xb5, 0xf4,
    0xcb, 0xfb, 0xf1, 0x0c, 0x2e, 0xa0, 0xd7, 0xc9, 0x1f, 0xd6, 0x06, 0x9a, 0x09, 0x41, 0x54,
    0x67, 0x46, 0xc7, 0x74, 0xe3, 0xc8, 0xb6, 0x5d, 0xa6, 0x36, 0xc4, 0xab, 0x2c, 0x7e, 0x85,
    0xa8, 0xa4, 0xa6, 0x4d, 0x96, 0x19, 0x19, 0x9a, 0xcc, 0xd8, 0xac, 0x39, 0x5e, 0x3c, 0xf2,
    0xf5, 0x5a, 0x72, 0xe5, 0xa9, 0xd1, 0xb3, 0x23, 0x82, 0x6f, 0x29, 0xcb, 0xd1, 0xcc, 0x71,
    0xfb, 0xea, 0x92, 0xeb, 0x1c, 0xca, 0x4c, 0x70, 0xfe, 0x4d, 0xc9, 0x67, 0x43, 0x47, 0x94,
    0xb9, 0x47, 0xbc, 0x3f, 0x01, 0xab, 0x7b, 0xa6, 0xe2, 0x76, 0xef, 0x5a, 0x7a, 0x29, 0x0b,
    0x51, 0x54, 0x67, 0xd8, 0x1c, 0x14, 0x3e, 0x29, 0xec, 0xe9, 0x2d, 0x48, 0x67, 0xff, 0xed,
    0x54, 0x4f, 0x48, 0xc0, 0xaa, 0x61, 0xf7, 0x78, 0x12, 0x03, 0x7a, 0x9e, 0x8b, 0xcf, 0x83,
    0x7b, 0xae, 0xca, 0x7b, 0xd9, 0xe9, 0x53, 0x2a, 0xeb, 0xd2, 0xd8, 0xcd, 0xa3, 0x10, 0x25,
    0x78, 0x5a, 0xb5, 0x23, 0x06, 0x93, 0xb7, 0x84, 0xd2, 0xbd, 0x96, 0x75, 0xa5, 0x5e, 0xcf,
    0x4e, 0xe9, 0x50, 0xa1, 0xe6, 0x9d, 0xb1, 0xe3, 0x85, 0x66, 0x28, 0x4e, 0x43, 0xdc, 0x6e,
    0xbb, 0x33, 0x9e, 0xf3, 0x0d, 0x00, 0xc1, 0xcf, 0x67, 0x34, 0x06, 0x7c, 0x71, 0xe3, 0x63,
    0xb7, 0xb7, 0xdf, 0x92, 0xc4, 0xc2, 0x25, 0x5c, 0xff, 0xc3, 0x6e, 0xfc, 0xaa, 0x1e, 0x2a,
    0x48, 0x11, 0x1c, 0x36, 0x68, 0x78, 0x86, 0x79, 0x30, 0xc3, 0xd6, 0xde, 0xbc, 0x3a, 0x2a,
    0x6d, 0x1e, 0x46, 0xdd, 0xe0, 0x80, 0x1e, 0x44, 0x3b, 0x6f, 0xaf, 0x31, 0xda, 0xa2, 0xbd,
    0x77, 0x06, 0x56, 0xc0, 0xb7, 0x92, 0x4b, 0x37, 0xc0, 0xfc, 0xc2, 0xd5, 0xfb, 0xa8, 0xda,
    0xf5, 0x57, 0xa8, 0x18, 0xc0, 0xdf, 0xe7, 0xaa, 0x2a, 0xe0, 0x7c, 0x6f, 0x77, 0xb1, 0x26,
    0xba, 0xf9, 0x2e, 0x1d, 0x16, 0xcb, 0xb8, 0xa2, 0x44, 0xd5, 0x2f, 0x1a, 0x79, 0x74, 0x87,
    0x4b, 0x00, 0xc9, 0x4a, 0x3a, 0x65, 0x8f, 0xe6, 0x5d, 0xe5, 0x0a, 0x77, 0xd8, 0x1a, 0x14,
    0x41, 0x75, 0xb1, 0xe2, 0x50, 0x2c, 0x93, 0x38, 0x2b, 0x6d, 0xf3, 0xf6, 0xdb, 0x1f, 0xcd,
    0xff, 0x14, 0x70, 0xe7, 0x16, 0xe8, 0x3d, 0xf0, 0xe3, 0xbc, 0x5e, 0xb6, 0x3f, 0xcc, 0x81,
    0x24, 0x67, 0xf3, 0x97, 0x3b, 0xfe, 0x3a, 0x96, 0x85, 0xdf, 0xe4, 0x6e, 0x3c, 0x85, 0x05,
    0x0e, 0xa3, 0x2b, 0x07, 0xc8, 0xbf, 0xe5, 0x13, 0x82, 0x62, 0x08, 0x61, 0x69, 0x4b, 0x47,
    0x62, 0x73, 0x44, 0x64, 0x8e, 0xe2, 0x91, 0xa6, 0x9a, 0xb7, 0xe9, 0x04, 0xb6, 0x54, 0x0c,
    0xc5, 0xa9, 0x47, 0xa6, 0xc9, 0x08, 0xfe, 0x4e, 0xa6, 0xcc, 0x8a, 0x5b, 0x90, 0x6f, 0x2b,
    0x3f, 0xb6, 0x0a, 0x96, 0xc0, 0x78, 0x58, 0x3c, 0x76, 0x6d, 0x94, 0x1a, 0xe4, 0x4e, 0xb8,
    0x38, 0xbb, 0xf5, 0xeb, 0x29, 0xd8, 0xb0, 0xf3, 0x15, 0x1e, 0x99, 0x96, 0x3c, 0x5d, 0x63,
    0xd5, 0xb1, 0xad, 0x52, 0xb8, 0x55, 0x70, 0x75, 0x3e, 0x1a, 0xd5, 0xda, 0xf6, 0x7a, 0x48,
    0x7d, 0x44, 0x41, 0xf9, 0x11, 0xce, 0xd7, 0xca, 0xa5, 0x3d, 0x7a, 0x79, 0x7e, 0x7d, 0x25,
    0x1b, 0x77, 0xbc, 0xf7, 0xc7, 0x0f, 0x84, 0x95, 0x10, 0x92, 0x67, 0x15, 0x11, 0x5a, 0x5e,
    0x41, 0x66, 0x0f, 0x38, 0x03, 0xb2, 0xf1, 0x5d, 0xf8, 0xab, 0xc0, 0x02, 0x76, 0x84, 0x28,
    0xf4, 0x9d, 0x56, 0x46, 0x60, 0x20, 0xdb, 0x68, 0xa7, 0xbb, 0xee, 0xac, 0x15, 0x01, 0x2f,
    0x20, 0x09, 0xdb, 0xc0, 0x16, 0xa1, 0x89, 0xf9, 0x94, 0x59, 0x00, 0xc1, 0x76, 0xbf, 0xc1,
    0x4d, 0x5d, 0x2d, 0xa9, 0x85, 0x2c, 0xd6, 0xd3, 0x14, 0xcc, 0x02, 0xc3, 0xc2, 0xfa, 0x6b,
    0xb7, 0xa6, 0xef, 0xdd, 0x12, 0x26, 0xa4, 0x63, 0xe3, 0x62, 0xbd, 0x56, 0x8a, 0x52, 0x2b,
    0xb9, 0xdf, 0x09, 0xbc, 0x0e, 0x97, 0xa9, 0xb0, 0x82, 0x46, 0x08, 0xd5, 0x1a, 0x8e, 0x1b,
    0xa7, 0x90, 0x98, 0xb9, 0xbb, 0x3c, 0x17, 0x9a, 0xf2, 0x82, 0xba, 0x64, 0x0a, 0x7f, 0xca,
    0x5a, 0x8c, 0x7c, 0xd3, 0x79, 0x09, 0x5b, 0x26, 0xbb, 0xbd, 0x25, 0xdf, 0x3d, 0x6f, 0x9a,
    0x8f, 0xee, 0x21, 0x66, 0xb0, 0x8d, 0x84, 0x4c, 0x91, 0x45, 0xd4, 0x77, 0x4f, 0xb3, 0x8c,
    0xbc, 0xa8, 0x99, 0xaa, 0x19, 0x53, 0x7c, 0x02, 0x87, 0xbb, 0x0b, 0x7c, 0x1a, 0x2d, 0xdf,
    0x48, 0x44, 0x06, 0xd6, 0x7d, 0x0c, 0x2d, 0x35, 0x76, 0xae, 0xc4, 0x5f, 0x71, 0x85, 0x97,
    0xc4, 0x3d, 0xef, 0x52, 0xbe, 0x00, 0xe4, 0xcd, 0x49, 0xd1, 0xd1, 0x1c, 0x3c, 0xd0, 0x1c,
    0x42, 0xaf, 0xd4, 0xbd, 0x58, 0x34, 0x07, 0x32, 0xee, 0xb9, 0xb5, 0xea, 0xff, 0xd7, 0x8c,
    0x0d, 0x2e, 0x2f, 0xaf, 0x87, 0xbb, 0xe6, 0x52, 0x71, 0x22, 0xf5, 0x25, 0x17, 0xa1, 0x82,
    0x04, 0xc2, 0x4a, 0xbd, 0x57, 0xc6, 0xab, 0xc8, 0x35, 0x0c, 0x3c, 0xd9, 0xc2, 0x43, 0xdb,
    0x27, 0x92, 0xcf, 0xb8, 0x25, 0x60, 0xfa, 0x21, 0x3b, 0x04, 0x52, 0xc8, 0x96, 0xba, 0x74,
    0xe3, 0x67, 0x3e, 0x8e, 0x8d, 0x61, 0x90, 0x92, 0x59, 0xb6, 0x1a, 0x1c, 0x5e, 0x21, 0xc1,
    0x65, 0xe5, 0xa6, 0x34, 0x05, 0x6f, 0xc5, 0x60, 0xb1, 0x83, 0xc1, 0xd5, 0xd5, 0xed, 0xd9,
    0xc7, 0x11, 0x7b, 0x49, 0x7a, 0xf9, 0xf9, 0x84, 0x47, 0x9b, 0xe2, 0xa5, 0x82, 0xe0, 0xc2,
    0x88, 0xd0, 0xb2, 0x58, 0x88, 0x7f, 0x45, 0x09, 0x67, 0x74, 0x61, 0xbf, 0xe6, 0x40, 0xe2,
    0x9d, 0xc2, 0x47, 0x05, 0x89, 0xed, 0xcb, 0xbb, 0xb7, 0x27, 0xe7, 0xdc, 0x7a, 0xfd, 0xbf,
    0xa8, 0xd0, 0xaa, 0x10, 0x39, 0x3c, 0x20, 0xf0, 0xd3, 0x6e, 0xb1, 0x72, 0xf8, 0xe6, 0x0f,
    0xef, 0x37, 0xe5, 0x09, 0x33, 0x5a, 0x83, 0x43, 0x80, 0x4f, 0x65, 0x2f, 0x7c, 0x8c, 0x6a,
    0xa0, 0x82, 0x0c, 0xd4, 0xd4, 0xfa, 0x81, 0x60, 0x3d, 0xdf, 0x06, 0xf1, 0x5f, 0x08, 0x0d,
    0x6d, 0x43, 0xf2, 0xe3, 0x11, 0x7d, 0x80, 0x32, 0xc5, 0xfb, 0xc5, 0xd9, 0x27, 0xec, 0xc6,
    0x4e, 0x65, 0x27, 0x76, 0x87, 0xa6, 0xee, 0xee, 0xd7, 0x8b, 0xd1, 0xa0, 0x5c, 0xb0, 0x42,
    0x13, 0x0e, 0x95, 0x4a, 0xf2, 0x06, 0xc6, 0x43, 0x33, 0xf4, 0xc7, 0xf8, 0xe7, 0x1f, 0xdd,
    0xe4, 0x46, 0x4a, 0x70, 0x39, 0x6c, 0xd0, 0xed, 0xca, 0xbe, 0x60, 0x3b, 0xd1, 0x7b, 0x57,
    0x48, 0xe5, 0x3a, 0x79, 0xc1, 0x69, 0x33, 0x53, 0x1b, 0x80, 0xb8, 0x91, 0x7d, 0xb4, 0xf6,
    0x17, 0x1a, 0x1d, 0x5a, 0x32, 0xd6, 0xcc, 0x71, 0x29, 0x3f, 0x28, 0xbb, 0xf3, 0x5e, 0x71,
    0xb8, 0x43, 0xaf, 0xf8, 0xb9, 0x64, 0xef, 0xc4, 0xa5, 0x6c, 0x08, 0x53, 0xc7, 0x00, 0x10,
    0x39, 0x4f, 0xdd, 0xe4, 0xb6, 0x19, 0x27, 0xfb, 0xb8, 0xf5, 0x32, 0x73, 0xe5, 0xcb, 0x32
};

/*
====================
COM_BlockSequenceCRCByte

For proxy protecting
====================
*/
byte COM_BlockSequenceCRCByte(byte *base, size_t length, int sequence)
{
    int     n;
    const byte  *p;
    int     x;
    byte chkb[60 + 4];
    unsigned short crc;

    if (sequence < 0)
        Com_Error(ERR_DROP, "%s: sequence < 0", __func__);

    p = chktbl + (sequence % (sizeof(chktbl) - 4));

    if (length > 60)
        length = 60;
    memcpy(chkb, base, length);

    chkb[length] = p[0];
    chkb[length + 1] = p[1];
    chkb[length + 2] = p[2];
    chkb[length + 3] = p[3];

    length += 4;

    crc = CRC_Block(chkb, length);

    for (x = 0, n = 0; n < length; n++)
        x += chkb[n];

    crc = (crc ^ x) & 0xff;

    return crc;
}

